International Patent Publication Nos. WO 96/15130 and WO 95/25106 discloses phenyloxazolidinone derivatives having a bicyclic thiazine or oxazine phenyl substituent. Some compounds possess useful antibacterial activity against Gram-positive bacteria such as Staphylococcus aureus and Streptococcus pneumonia. However, these compounds are less antibacterially effective than well-known antibiotic vancomycin.
The present inventors conducted a long intensive investigation for the development of novel oxazolidinone compounds which have superior activity against Gram-positive bacteria to the well-known antibiotic vancomycin. Novel oxazolidinone derivatives having bicyclic substituents, which are structurally distinguished from those as disclosed in International Patent Publication Nos. WO 96/15130 and WO 95/25106 have now been developed. It was found that the present novel oxazolidinone derivatives possesses almost same or higher antibacterial activity against a variety of Gram-positive bacteria compared to the well-known antibiotic vancomycin.